SMTP Relay doesn't have Let's Encrypt integration yet. Currently, it is using a Self-Signed SSL for SMTP Relay.

One potential solution is to implement an ACME (Automated Certificate Management Environment) Docker container. This can be achieved through an ez_install wizard, simplifying the installation process.

After the post-installation of the ACME Docker container, users could be prompted to configure Let's Encrypt SSL. This could be done through either HTTP verification or by utilizing the CloudFlare DNS API for added flexibility. The implementation of Let's Encrypt SSL would replace the current WebUI and TLS SSL configuration.